Just thought I'd post this as a bit of encouragment to others who are having the same problems. I've posted on a few threads recently about DD sitting/standing up in her cot when sh'es meant to be asleep, both asking for and offering help.
Well today she did it!! She lay down herself! I put her in her cot and left her for a while, I peeked in and she was standing up, but I left her again, she didn't spot me. I've just crept in again and there she was sleeping soundly! i'm so proud of her!
So hang in there all of you, they can do eventually!!